The present invention relates to gravity fed intravenous delivery systems and, in particular, it concerns a system for metering and regulating the fluid flow thereof.
A typical gravity fed intravenous system may be as simple as an IV bag hanging on a pole and a medical staff person manually adjusting a valve to limit the flow rate, but not control it accurately. Traditionally, the flow rate of the fluid from the IV bag was roughly measured with a drip chamber at the IV bag and controlled by a clamp varying the restriction in a delivery line extending between the drip chamber and the patient. A medical staff person visually counts the drop rate in the drip chamber and manually sets the clamping or pinching device to achieve a desired flow rate. The accuracy of this system assumes the consistency in volume of each drop of fluid into the drip chamber. However, the drop size is dependent on the orifice diameter, the inner and the outer diameter of the tip in the drip chamber, which varies within a manufacturing tolerance for a particular container. Even the nominal orifice diameter is not uniform throughout the industry. Manufacturers sell drip chambers having 10, 15, 20 and 60 drop per milliliter chambers, for example. In addition, the volume of the drops may vary with temperature, viscosity and rate. Further, the rate remains essentially constant as long as the head of liquid does not change appreciably. Of course, as the liquid is being fed to the patient, the pressure head slowly decreases causing the flow rate to decrease proportionately, and if a precise amount of liquid is to be supplied to the patient, this change must be taken into account when the valve is initially set, or in the alternative, the manual valve can be reset from time to time. However, should the patient roll over or make some other movement, which appreciably changes the vertical distance between the IV bag and the catheter, the flow rate changes more dramatically.
There have been numerous proposals in prior art for devices that do not rely on gravity as the driving force for the flow of fluid through the system. These systems include the use of pump devices or devices that apply pressure directly to the IV bag in order to create and maintain a predefined head pressure. The pressurized fluid is then regulated. This group is characterized by various styles of peristaltic-type infusion pumps, which manipulate the fluid flow in the delivery line. There a several problems associated with these non-gravity fed devices. They provide fluid medication to the patient at high pressure this may result in physical damage to the vein or artery of the patient. With pressurization comes the chance of bubbles in the system, and these devices must include bubble detectors. Their complexity of design results in complex operation that may increase the opportunity for malfunction and the need for enough energy to power the device. The need for energy usually requires that the device be plugged into a wall outlet, there by restricting the mobility of the patient while receiving treatment. Further, the intricacy of manufacture results in high purchase costs to the consumer, i.e. hospitals and clinics, which generally have tight and limited budgets. Therefore, these devices are available in relatively limited quantities and used on a xe2x80x9cmost needed casexe2x80x9d basis.
The devices of U.S. Pat. No. 4,207,871 to Jenkins and U.S. Pat. No. 4,559,044 to Robinson, et al. are attempts to utilize relatively small pumps. These are still active pumps and suffer from all of problems enumerated above.
Returning now to gravity fed systems. As mentioned above, the most common way of metering the fluid flow in a gravity fed intravenous system is for a medical staff person to manually count drops, readjusting a flow adjustment valve as needed throughout the fluid delivery process. One attempted method to overcome the obvious problems of this manner of flow metering has been by the use of optical drop counters. While this provides a means of substantially constant monitoring not available from human staff, the problems of drop size and fluid viscosity still exist since this is still just counting the drops.
There is therefore a need for a low cost fluid flow meter for use with gravity fed intravenous fluid delivery systems that is unaffected by the properties of the intravenous system to which it is attached, i.e. changing head pressure, that is accurate regardless of any physical properties of a particular fluid, i.e. viscosity, and specific density, and that is able to adjust the flow rate as necessary to maintain a prescribed flow rate. It would be preferable that the components of the system that come in contact with the fluid be made disposable.
The present invention is a flow metering system for accurately metering and regulating the flow rate of fluid in a gravity fed intravenous fluid delivery system.
According to the teachings of the present invention there is provided, a flow meter for achieving an accurate reading of the flow rate of a fluid, the flow meter comprising: a) a fluid flow path guide along which the fluid flows, the flow path guide being deployed at an angle with an upper end fixedly attached to a meter inlet and a lower end suspended above a reservoir attached to a meter outlet, the flow path guide having an initial position, the flow path guide configured so as to have a given elastic resiliency such that when bent and subsequently released the flow path guide returns to the initial position; b) a sensing device configured and deployed so as to generate an output which varies as a function of movements of the flow path guide; and c) a processing unit in electronic communication with the sensing device, the processing unit configured to use the output from the sensing device to determine the flow rate.
According to a further teaching of the present invention, the given elastic resiliency is inherent to the configuration of the flow path guide.
According to a further teaching of the present invention, the flow path guide includes a conduit that is substantially closed along a dimension called length, the conduit being open to fluid flow at each of two ends.
According to a further teaching of the present invention, the flow path guide includes a helical spring.
According to a further teaching of the present invention, the given elastic resiliency is inherent to a material from which the flow path guide is fabricated.
According to a further teaching of the present invention, the given elastic resiliency is inherent to a material from which an element, to which the flow path guide is attached, is fabricated.
According to a further teaching of the present invention, the sensing device includes at least one magnetic sensor.
According to a further teaching of the present invention, the sensing device includes an optical sensor.
According to a further teaching of the present invention, at least one property that enables the sensing device to discern the movements of the flow path guide is inherent to a material from which the flow path guide is fabricated.
According to a further teaching of the present invention, at least one property that enables the sensing device to discern the movements of the flow path guide is inherent to a material that is affixed to the flow path guide.
According to a further teaching of the present invention, the flow path guide, the sensing device and the processor are housed in a single housing.
According to a further teaching of the present invention, the flow path guide is deployed within a housing, the housing including the meter inlet and the meter outlet, and the sensing device and the processor are removably interconnected with the housing.
There is also provided according to the teachings of the present invention, a flow metering system for accurately metering and regulating the flow rate of fluid flowing through a tube of a fluid delivery system, the flow metering system comprising: a) an adjustable flow regulator assembly having a regulator inlet, the flow regulator thereby receiving a flow of fluid, the flow regulator being configured so as to regulate the flow of fluid through the regulator, the regulator including an adjustment mechanism responsive to an adjustment actuator, the flow regulator further having a regulator outlet; and b) the flow meter of claim 1 in fluid communication with the regulator; wherein the adjustment actuator is in electronic communication with, and responsive to, the processing unit, so as to regulate the flow.
According to a further teaching of the present invention, the fluid delivery system includes a gravity fed intravenous fluid delivery system for delivery of fluid drugs to a patient.
According to a further teaching of the present invention, the flow regulator assembly includes a variable length elongated flow path.
According to a further teaching of the present invention, the adjustment mechanism is configured so as to vary length of the elongated flow path.
According to a further teaching of the present invention, the processing unit, and the adjustment actuator are included in a base housing unit.
According to a further teaching of the present invention, at least part of the flow regulator and at least part of the flow meter are included in a removable fluid flow path unit.
There is also provided according to the teachings of the present invention, a flow metering method for accurately metering the flow rate of fluid flowing through a tube of a fluid delivery system, the flow metering method comprising: a) directing the flow along a fluid flow path guide, the flow path guide being deployed at an angle with an upper end fixedly attached to a meter inlet and a lower end suspended above a reservoir attached to a meter outlet, the flow path guide having an initial position, the flow path guide configured so as to have a given elastic resiliency such that when bent and subsequently released the flow path guide returns to the initial position, the bending being caused by weight from a build up of fluid at a lower end and the return of the flow path guide to the initial position occurring when a drop is released from the lower end of the flow path guide; b) sensing movements of the flow path guide; and c) processing output resulting from the sensing, so as to derive fluid flow rate.
According to a further teaching of the present invention, the flow is regulated based on the processing.
According to a further teaching of the present invention, the regulating is accomplished by varying the length of a variable length elongated flow path.
According to a further teaching of the present invention, the varying is accomplished by activation of an adjustment actuator.
According to a further teaching of the present invention, the activation includes activation of an electric-motor-driven gear assembly.
According to a further teaching of the present invention, the regulation maintains a predetermined flow rate.
According to a further teaching of the present invention, the regulation changes the flow rate according to a predefined program.